南堡地区碳酸盐岩储层孔隙结构特征及对物性的影响

Pore Structure Characteristics and Their Influence on Petrophysical Properties of Carbonate Reservoirs in the Nanpu Area

利用数字图像分析法对南堡地区碳酸盐岩储层的孔隙结构参数进行定量求取,明确了不同类型孔隙的孔隙结构参数特征,分析了孔隙结构特征对储层物性的影响,并应用优选出的孔隙结构参数建立碳酸盐岩储层物性预测模型。结果表明:研究区内碳酸盐岩储层的储集空间以次生孔隙为主,为一套典型的孔隙型储层。应用孔隙结构参数可以较好的区分铸模孔、粒间孔、粒内孔和晶间孔等孔隙类型,其中铸模孔呈较低的平均等效直径与高的宽纵比,粒间孔以高等效直径25%为特征,粒内孔对应最低的比表面、最高的等效直径标准差,晶间孔比表面较高且宽纵比分布范围局限。等效直径、形状因子、球度和宽纵比等参数对储层物性的影响显著。分别针对孔隙度和渗透率,在提取的28项孔隙结构参数中优选出6种相关性高的参数,并应用多元线性回归方法分别进行拟合。验证结果显示拟合公式具有较高的可信度,且渗透率(R^2=0.916)优于孔隙度(R^2=0.778)。该方法可为研究区及其他地区的孔隙型碳酸盐岩储层评价研究提供参考。

The pore structure parameters of carbonate rocks is quantified by digital image analysis (DIA) to determine the characteristics of the pores in this complex structure and their influence on its physical properties. A model for predicting the physical properties of the carbonate reservoir is established after selecting appropriate parameters. The carbonate reservoir is a typical porous reservoir dominated by secondary pores. Application of pore-structure parameters in this way enables the various pore types in the carbonate reservoirs in the Nanpu area to be distinguished. Pore types included: moldic pores with low perimeter-over-area (PoA) and high aspect ratio;intergranular pores with low PoA and high equivalent diameter (the latter having a large standard deviation);and matrix pores, typically of high PoA and high average equivalent diameter. Of all the pore parameters, the equivalent diameter, form factor, roundness and compactness are found to have the greatest effect on porosity and permeability. Further, 28 parameters are optimized by means of correlation matrix. The best-fit relationship between pore structure parameters and porosity and permeability is established by multivariate linear regression, giving the very reasonable R 2 values of 0.778 for porosity and 0.916 for permeability. These results provide an ideal reference for evaluating the properties of porous carbonate reservoirs in Nanpu and in other areas.